BT “MAUD” Multicast Streaming Breakthrough- reducing lag?

[SPORTSLJM]

@DarrenDev if this is the case that it’s the encoding etc that takes the time or causes the delay in delivery to screen, how does BTs multicast manage to deliver their TV product within around 8-10seconds of Satellite compared to other stream tv options? 

[DarrenDev]

There's no repackaging for multicast - it's video stream direct to video stream. ABR means chopping the video into segments (between 2 and 6 seconds long), encoding at multiple quality levels and multiple formats, DRM protecting each chunk, and adding to the manifest. Clients then load/refresh that manifest every few seconds and wait until there are sufficient chunks to play seamlessly. e.g. some clients would be capable of playing nearer to the live point, but they choose to stay a few seconds behind so that they can offer smooth playback if any segments are delayed. If a segment was requested just as the connection briefly dropped, it'd take a couple of seconds to timeout, and then the client needs to request the next level down ... if the player was at the live point, you'd see buffering. By intentionally being slightly behind, it can show the lower quality briefly and then go back up when it's proven the connection is stable again.
With multicast, none of this happens - the bandwidth is guaranteed, so there's only a single quality available. Delivery is also marked top priority over the network, so if data is dropped the picture breaks up briefly and then resumes when it can.

A massive over-simplification, but hopefully enough to illustrate the difference.

Google for low latency ABR to find a few articles out there about what it offers.

[naylor2006]

@DarrenDev so how does this breakthrough differ from the existing Multicast service hitting my EE/BT TV Box Pro? Is it a different type of multicast pointing towards app based content and not live TV?

Also a side question, I use my own router which uses a IGMP proxy which works perfectly for my BT TV Box Pro, I assume it wont alter that side of things?

[DarrenDev]

Yes - MAUD is about delivering "over the top" content to apps, where multiple people would be watching the same thing at the same time.  e.g. any of the live channels in any of the apps, across any devices.  Multicast is a very specific technology that only works in controlled situations (which is why it has been so hard to get other routers working).

MAUD is being pushed as an open standard, so hopefully 3rd party routers will adopt it.  Where incompatible routers are used, the service will continue to work as they currently do.  MAUD on the router will be transparent to the user - routers will just optimise traffic where they can.

[naylor2006]

Oh I see, thanks for the explanation, so as far as watching live channels on the BT Box which is using Multicast Streaming this will be unaffected.

Its more for the 10 people in one house watching live TV via BBC iPlayer the content is only delivered once?

[DarrenDev]

Yes, that's an extreme example affecting just you in the home. The benefit is at the wider scale though - the core network across the UK. If all the network bandwidth is consumed by so many million people watching the Olympics opening ceremony on Freely (which will deliver channels the same way that iPlayer does), then there's no internet left for anything else.

[Crimliar]

The conversation seems to be going off on a tangent here.  BT have not just invented "multicasting" - that was first standardised back in 1986and most consumer routers and streaming devices have no issue with multicast streams.  MAUD if my understanding is correct is about how those streams are bundled together and distributed across the internet backbone - you won't be getting that fat pipe of streams sent down every household tributary of the internet.

[DarrenDev]

MAUD is about using Multicast to carry live Unicast streams across the network core.  That's the new bit @Crimliar 

[naylor2006]

Yeah, I was just trying to understand the difference between the existing Multicast methods and MAUD, that was the basis behind my question. Indeed I am aware Multicast has been around for yonks!